Present hip prosthesis rehabilitation procedures cannot be based on their induced force and pressure stresses: no such direct in vivo data exist to guide clinicians, so current exercise and Activities of Daily Living recommendations rely on indirect evidence. This proposal addresses two broad research questions: 1) Do current rehabilitation protocols for acutely painful hips in fact increment femoro-acetabular stresses as clinicians expect? 2) Are strength and mobility exercises for subacute and chronic hip arthritis more or less stressful than daily activities such as transfers and walking? Six patients with intact acetabular cartilage will receive a force and pressure-instrumented Austin-Moore endoprosthesis. Simultaneous hip forces and pressures, kinematic and kinetic data will be collected in the hospital and after discharge in the gait laboratory. Experiments examining acutely painful hip arthritis rehabilitation protocols will be conducted during the recovery phase; exercise and ADL protocols now used in subacute and chronic hip arthritis rehabilitation will be assessed more than 6 months following implantation. The present proposal builds upon A) our in vivo hip pressure-only research; B) the protocols and instrumentation developed during prior funding periods; and C) currently approved NIH funding for equipment and engineering personnel to fabricate, implant and collect data from 6 new force and pressure instrumented endoprostheses. These other projects, however, do not fund the clinical personnel necessary to devise, conduct and report the results of empirical experiments based on rehabilitation practices. We request funding to address directly-for the first time, with data from living humans-the acetabular forces and pressures induced by rehabilitation procedures in patients with hip joint impairments.